RFR [11]: Fix post-merge build problem: Shenandoah should be disabled with Zero

[Aleksey Shipilev]

Build-test shows I did a little merge mistake in sh/jdk11: I forgot to add shenandoahgc to the new
block that disables Zero for all unsupported GCs.

Here is the rectification:

diff -r 3f6d0b57c622 make/autoconf/hotspot.m4
--- a/make/autoconf/hotspot.m4  Tue Mar 05 20:27:45 2019 +0100
+++ b/make/autoconf/hotspot.m4  Wed Mar 06 18:00:55 2019 +0100
@@ -356,11 +356,11 @@
     AC_MSG_RESULT([no, platform not supported])
   fi

   # Disable unsupported GCs for Zero
   if HOTSPOT_CHECK_JVM_VARIANT(zero); then
-    DISABLED_JVM_FEATURES="$DISABLED_JVM_FEATURES epsilongc g1gc zgc"
+    DISABLED_JVM_FEATURES="$DISABLED_JVM_FEATURES epsilongc g1gc shenandoahgc zgc"
   fi

   # Turn on additional features based on other parts of configure
   if test "x$INCLUDE_DTRACE" = "xtrue"; then
     JVM_FEATURES="$JVM_FEATURES dtrace"

Testing: local x86_64-zero build

-Aleksey